The broad, long-term objective of the research is to develop a biosensor platform that can be adapted to detection of a wide variety of pathogens, toxins, and biological molecules. The immediate application is to cryptosporidium, a protozoan that is a common, naturally occurring contaminant of public water supplies. It is also a potential bio-terror agent that could cause serious illness with many deaths among the elderly, infants, and immunocompromised individuals. The project aims specifically to identify DNA "c-probe" sequences from pools of billions or trillions of candidates that have high affinity for cryptosporidium and adapting the high affinity binding sequnces into a fluorescent biosensor. A protocol is described that should allow efficient discovery of these sequences within days, as opposed to the current practice that often requires months of effort by skilled practitioners. Development of a high throughput screening method that is much faster and more versatile than the existing methods, coupled with novel pyrosequencing technology will be key in the excution of the proposal's main objectives.